Color television tube



Mam]! 1951 A. c. SCHROEDER COLOR TELEVISION TUBE Filed June 11, 1946 INV E N TO R 4L FRED 6- Jamozom Patented Mar. 20,1951

Alfred G. Schroeder,- Feastei-ville,

Radio Corporation of America,

Delaware Pa., assignor to a corporation of Application June 11, 1946,Serial No. 675,861

6 Claims.

This invention relates to cathode ray tubes for producing coloredpictures.

Colored pictures have been produced by cathode ray tubes by rotatingcolor filters in front of the fluorescent screen of a tube in synchroanism with the production of color signals at the pick-up tube, butrotating parts in a television system are objectionable and should beavoided wherever possible.

It is an object of this invention to produce colored television pictureswithout mechanically moving parts. 7

Another object of the invention is to produce colored pictures solely byelectron means.

Another object of the invention is to produce colored pictures bypassing white light through an alkali metal halide target of a cathoderay beam tube and producing in the target a series of laminar darktraces spaced apart to produce color by light Wave interference.

Other objects of the invention will appear in the followingspecification, reference being had to the drawings, in which:

Figure 1 is a sectional view of a cathode ray beam tube of my invention.

Figure 2 is an enlarged section of the screen illustrating the theory ofoperation.

It is well known that an alkali halide screen exhibits dark traces underbombardment by electrons, such as produced by a cathode ray beam. It isnow generally thought that these dark traces are produced-by electronsbombarded from the crystal lattice of the halide anion and that thesedisplaced electrons absorb energy from light incident thereon, whichmoves the electrons to a place in the screen having excess of positivepotential. This excess of positive potential may be due to non-uniformdistribution of the positive alkali cations, or it may be produced byelectric fields applied to the screen for this purpose. As heretoforeused, particularly in radar, the dark traces were used merely to producevisible signals giving position of an object and the movement of theelectrons back to a bound position in the lattice had no function exceptto determine the length of time the dark trace was visible. In myinvention I cause the electrons to move through the screen in successivewaves, so that the series of dark sheets in the target product lightwave interference that enables one to produce any desired color bycontrol of the frequency of production of such lines.

Any desired tube may be used for producing colored pictures, but in Fig.1 I have shown more or less schematically a tube having my improvedtarget T. This tube has the usual evacuated envelope l containing ascreen electrode 2 having a slit aperture, a grid electrode 3, anindirectly heated cathode 4 shown grounded and a first anode 5. A secondanode 6 may also be used. In front of the second anode 6 may be placedelectrostatic vertical deflection plates 1 and 8 for scanning thecathode ray beam vertically over the raster of the target T, line byline. No horizontal deflection is required, as the beam is spreadout thefull length of a line, as by use of long slits for apertures in thevarious electrodes, or in any other way. The beam is preferably thickenoughto cover several lines in avertical direction of the target.

The target T may consist of a plate 9 of any alkali metal halide, suchas potassium chloride, for example. Preferably, the target also has atransparent metal film H] in front of the potassium chloride plate,which has a suitable positive potential applied theretofor controllingthe passage of the sheet of electrons through the plate.

The operation of the invention is as follows:

A suitable generator H is connected to the grid 3 to block the cathodebeam or otherwise vary its intensity at definite frequencies. As thebeam sweeps from top to bottom over the poi-Jas siu'm chloride screen 9,electrons enter the screen and these, or electrons displaced thereby, orboth, move toward the positive plate l0. These elec trons absorb lightenergy coming from the fluorescent screen E2 of kinescope I3 and producedark traces, which are viewed by the observers eye at E. Theinterruption of the beam by the grid produces a series of electronsmoving in spaced sheets I4 toward the positive plate It]. When thecathode beam is interrupted or other wise modulated at a certainfrequency while the beam covers each element area of the raster, thespacing of the sheets M in the target screen will produce interferenceto'the' light passing through the target and a certain color will beproduced, say red, as in the well-known Lippmann' system of colorphotography. By changing the frequency of the generator H, the frequencyof production of free electrons, and therefore the spacing of the darksheets, moving through the screen 9 will be changed to another distance,which will produce by interference another color, say green. In thisway, one produces color from white light coming from the kinescopephosphor screen l2.

Usually a transmitting pick-up tube scans an object to be televised onecomplete frame for transmitting signals proportional to, say, the redcolors in the object. At the receiver the generator H would becontrolled in synchronism with the distant pick-up tube, so that itlikewise would maintain the frequency of interruption of the cathode raybeam for one complete frame scansion. Then, during the next framescansion at the transmitter, the generator II at the receiver would beoperated to interrupt the cathode ray beam at a frequency to produce thecolor being televised by the pick-up tube, say green. In the nextscansion, if blue is being transmitted from the pick-up tube, thegenerator I l will operate at such frequency that the interferenceproduced by the dark sheets [4 in the target will produce blue color.

While I have described potassium chloride as the alkali halide fromwhich thedark trace target is constructed, it may be also constructed ofthe fluorides, chlorides, bromides and iodides of lithium, sodium,potassium, rubidium and caesium, asthese are known to produce similarresults. Also, other ways of producing interfering barriers to lightwaves may be employed in cathode ray tubes for converting white light tovarious 'colors.

I claim:

1. A color television device comprising, a cathode ray beam tube havingan alkali halide target, and a'cathode ray beam gun, field producingmeans for scanning the beam of said gun over one surface of said targetto produce dark traces at said, surface, a transparent positivepotential electrode on the other surface of the target, means connectedto said cathode ray beam gun for interrupting the beam a predeterminedconstant frequency during one scansion of the beam over the target andat a different constant frequency during each of a predetermined 'numberof successive scansions and a source of polychromatic light positionedto pass light through the target.

2. The method of producing color television pictures, said methodcomprising the steps of, successively scanning a cathode ray beam ofconstant intensity over one side of an alkali halide target,interrupting the electron beam at different predetermined frequencieswhile the beam covers each elemental area of said target surface, andsimultaneously passing a visual image of substantially white lightthrough said target to produce a colored picture of said image.

' 3. The method of producing a colored television picture from black andwhite images produced on the luminescent screen of a television tube,said method comprising the steps of, passing the light of said black andwhite images through an alkali halide target, scanning one side of saidalkali halide target with a cathode ray beam of constant intensity,interrupting the electron beam at different predetermined frequencieswhile the beam covers each elemental area of said target surfacethroughout respectively each of said scansions to produce a coloredpicture of said images.

4 producing on a white luminescent screen of a television viewing tube avisual image on each frame scansion corresponding respectively to adifferent color signal, passing the light of said images through analkali halide target, scanning in synchronism with the frame scanning ofthe television viewing tube one side of said alkali halide target with acathode ray beam to produce dark traces on said target surface,sequentially interrupting said cathode ray beam at a constant frequencyfor each frame scansion of said viewing tube, the frequency ofinterruption for each frame scansion differing from each of the others,and producing an electric field at the other surface of the target tomove said dark traces through said target,

, 5. A color television device comprising, a light I valve tubeincluding an alkali halide target and electron gun for producing anelectron beam within said tube, field producing means for frame scanningthe electron beam over one surface of said target to produce dark tracesat said surface, a transparent electrode on the other surface of saidtarget, lead means contacting said electrode for connecting saidtransparent electrode to a source of potential during tube operation, tomove the dark traces through said target,

I a, source of modulated polychromic light positioned to pass lightthrough said target, and means connected to said electron gun forinterrupting said .beam at predetermined frequencies for each framescanning of said target.

6. A color television device comprising, a light valve tube includinganalkali halide target and electron gun' for. producing an electron beamwithin said tube, field producing means for frame scanning the electronbeam over one surface of said target to produce dark traces at saidsurface, a transparent electrode on the other surface of said target,lead means contacting said electrode for connecting said transparentelectrode to a source of potential during tube operation, to move thedark traces through said target, a television viewing tube having awhile fluorescent screen and means responsive to sequential televisioncolor signals for producing on said fluorescent screen during each framescansion of said halide target an image corresponding to signalsrepresenting a single color, and means connected to said electron gunfor interrupting said beam at predetermined frequencies for each framescanning of said targets.

4. The method of producing color television ALFRED C. SCHROEDER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,109,540 Leishman Mar. 1, 19382,330,172 Rosenthal Sept. 21, 1943 FOREIGN PATENTS Number Country Date473,061 Great Britain Oct. 5, 1937

